| java.lang.Object
 org.jgroups.Channel
All known Subclasses: org.jgroups.JChannel,
| Channel | | abstract public class Channel implements Transport(Code) | | A channel represents a group communication endpoint (like BSD datagram sockets). A
client joins a group by connecting the channel to a group address and leaves it by
disconnecting. Messages sent over the channel are received by all group members that
are connected to the same group (that is, all members that have the same group
address).
The FSM for a channel is roughly as follows: a channel is created
(unconnected). The channel is connected to a group
(connected). Messages can now be sent and received. The channel is
disconnected from the group (unconnected). The channel could now be connected to a
different group again. The channel is closed (closed).
Only a single sender is allowed to be connected to a channel at a time, but there can be
more than one channel in an application.
Messages can be sent to the group members using the send method and messages
can be received using receive (pull approach).
A channel instance is created using either a ChannelFactory or the public
constructor. Each implementation of a channel must provide a subclass of
Channel and an implementation of ChannelFactory.
Various degrees of sophistication in message exchange can be achieved using building
blocks on top of channels; e.g., light-weight groups, synchronous message invocation,
or remote method calls. Channels are on the same abstraction level as sockets, and
should really be simple to use. Higher-level abstractions are all built on top of
channels.
author:
Bela Ban
See Also: java.net.DatagramPacket
See Also: java.net.MulticastSocket |
| Method Summary | |
| public synchronized void | addChannelListener(ChannelListener listener)
Allows to be notified when a channel event such as connect, disconnect or close occurs.
E.g. | | abstract public void | blockOk()
Called to acknowledge a block() (callback in MembershipListener or
BlockEvent received from call to Receive). | | abstract public void | close()
Destroys the channel and its associated resources (e.g., the protocol stack). | | abstract public void | connect(String cluster_name)
Connects the channel to a group. | | abstract public boolean | connect(String cluster_name, Address target, String state_id, long timeout)
Connects the channel to a group and fetches the state
Parameters:
cluster_name -
Parameters:
target -
Parameters:
state_id - The ID of a substate. | | abstract public void | disconnect()
Disconnects the channel from the current group (if connected), leaving the group.
It is a null operation if not connected. | | public void | down(Event evt)
Access to event mechanism of channels. | | public String | dumpQueue()
| | abstract public Map | dumpStats()
Returns a map of statistics of the various protocols and of the channel itself.
Map. | | abstract public boolean | flushSupported()
| | abstract public boolean | getAllStates(Vector targets, long timeout)
Retrieve all states of the group members. | | abstract public String | getChannelName()
Returns the group address of the group of which the channel is a member. | | abstract public String | getClusterName()
Returns the cluster name of the group of which the channel is a member. | | abstract public Address | getLocalAddress()
Returns the channel's own address. | | abstract protected Log | getLog()
| | public int | getNumMessages()
Returns the number of messages that are waiting. | | abstract public Object | getOpt(int option)
Gets an option. | | abstract public boolean | getState(Address target, long timeout)
Retrieve the state of the group. | | abstract public boolean | getState(Address target, String state_id, long timeout)
Fetches a partial state identified by state_id. | | abstract public View | getView()
Gets the current view. | | abstract public boolean | isConnected()
Determines whether the channel is connected to a group. | | abstract public boolean | isOpen()
Determines whether the channel is open;
i.e., the protocol stack has been created (may not be connected though). | | protected void | notifyChannelClosed(Channel c)
| | protected void | notifyChannelConnected(Channel c)
| | protected void | notifyChannelDisconnected(Channel c)
| | protected void | notifyChannelReconnected(Address addr)
| | protected void | notifyChannelShunned()
| | public void | open()
Re-opens a closed channel. | | public static String | option2String(int option)
| | abstract public Object | peek(long timeout)
Returns the next message, view, block, suspect or other event without removing
it from the queue.
Parameters:
timeout - Value in milliseconds. | | abstract public Object | receive(long timeout)
Receives a message, a view change or a block event. | | public synchronized void | removeChannelListener(ChannelListener listener)
| | abstract public void | returnState(byte[] state)
Called by the application is response to receiving a
getState() object when calling receive(). | | abstract public void | returnState(byte[] state, String state_id)
| | abstract public void | send(Message msg)
Sends a message to a (unicast) destination. | | abstract public void | send(Address dst, Address src, Serializable obj)
Helper method. | | public void | setChannelListener(ChannelListener channel_listener)
Allows to be notified when a channel event such as connect, disconnect or close occurs.
E.g. | | abstract public void | setOpt(int option, Object value)
Sets an option. | | public void | setReceiver(Receiver r)
| | public void | setUpHandler(UpHandler up_handler)
When up_handler is set, all events will be passed to it directly. | | abstract protected void | shutdown()
| | abstract public boolean | startFlush(long timeout, boolean automatic_resume)
| | abstract public void | stopFlush()
|
| AUTO_GETSTATE | | final public static int AUTO_GETSTATE(Code) | | |
| AUTO_RECONNECT | | final public static int AUTO_RECONNECT(Code) | | |
| BLOCK | | final public static int BLOCK(Code) | | |
| GET_STATE_EVENTS | | final public static int GET_STATE_EVENTS(Code) | | |
| LOCAL | | final public static int LOCAL(Code) | | |
| SUSPECT | | final public static int SUSPECT(Code) | | |
| VIEW | | final public static int VIEW(Code) | | |
| channel_listeners | | protected Set channel_listeners(Code) | | |
| addChannelListener | | public synchronized void addChannelListener(ChannelListener listener)(Code) | | Allows to be notified when a channel event such as connect, disconnect or close occurs.
E.g. a PullPushAdapter may choose to stop when the channel is closed, or to start when
it is opened.
|
| blockOk | | abstract public void blockOk()(Code) | | Called to acknowledge a block() (callback in MembershipListener or
BlockEvent received from call to Receive).
After sending BlockOk, no messages should be sent until a new view has been received.
Calling this method on a closed channel has no effect.
|
| close | | abstract public void close()(Code) | | Destroys the channel and its associated resources (e.g., the protocol stack). After a channel
has been closed, invoking methods on it throws the ChannelClosed exception
(or results in a null operation). It is a null operation if the channel is already closed.
If the channel is connected to a group, disconnec()t will be called first.
|
| connect | | abstract public void connect(String cluster_name) throws ChannelException, ChannelClosedException(Code) | | Connects the channel to a group. The client is now able to receive group
messages, views and block events (depending on the options set) and to send
messages to (all or single) group members. This is a null operation if already
connected.
All channels with the same name form a group, that means all messages
sent to the group will be received by all channels connected to the same
channel name.
Parameters:
cluster_name - The name of the chanel to connect to.
exception:
ChannelException - The protocol stack cannot be started
exception:
ChannelClosedException - The channel is closed and therefore cannot be used any longer.A new channel has to be created first.
See Also: Channel.disconnect |
| connect | | abstract public boolean connect(String cluster_name, Address target, String state_id, long timeout) throws ChannelException(Code) | | Connects the channel to a group and fetches the state
Parameters:
cluster_name -
Parameters:
target -
Parameters:
state_id - The ID of a substate. If the full state is to be fetched, set this to null
Parameters:
timeout - True if the state could be fetched, otherwise false. If true is returned, the state setting method (e.g.setState() will be called.
throws:
ChannelException - |
| disconnect | | abstract public void disconnect()(Code) | | Disconnects the channel from the current group (if connected), leaving the group.
It is a null operation if not connected. It is a null operation if the channel is closed.
See Also: Channel.connect(String)
See Also: |
| down | | public void down(Event evt)(Code) | | Access to event mechanism of channels. Enables to send and receive events, used by building
blocks to communicate with (building block) specific protocol layers. Currently useful only
with JChannel.
|
| dumpStats | | abstract public Map dumpStats()(Code) | | Returns a map of statistics of the various protocols and of the channel itself.
Map. A map where the keys are the protocols ("channel" pseudo key isused for the channel itself") and the values are property maps. |
| flushSupported | | abstract public boolean flushSupported()(Code) | | |
| getAllStates | | abstract public boolean getAllStates(Vector targets, long timeout) throws ChannelNotConnectedException, ChannelClosedException(Code) | | Retrieve all states of the group members. Will contact all group members to get
the states. When the method returns true, a SetStateEvent will have been
added to the channel's queue, causing Receive to return the states in one of
the next invocations. If false, no states will be retrieved by Receive.
Parameters:
targets - A list of members which are contacted for states. If the list is null,all the current members of the group will be contacted.
Parameters:
timeout - Milliseconds to wait for the response (0 = wait indefinitely). boolean True if the state was retrieved successfully, otherwise false.
exception:
ChannelNotConnectedException - The channel must be connected toreceive messages.
exception:
ChannelClosedException - The channel is closed and therefore cannot be usedany longer. A new channel has to be created first. |
| getChannelName | | abstract public String getChannelName()(Code) | | Returns the group address of the group of which the channel is a member. This is
the object that was the argument to connect(). Calling this method on a closed
channel returns null.
The group addressChannel.getClusterName() |
| getClusterName | | abstract public String getClusterName()(Code) | | Returns the cluster name of the group of which the channel is a member. This is
the object that was the argument to connect(). Calling this method on a closed
channel returns null.
The cluster name |
| getLocalAddress | | abstract public Address getLocalAddress()(Code) | | Returns the channel's own address. The result of calling this method on an unconnected
channel is implementation defined (may return null). Calling this method on a closed
channel returns null.
The channel's address. Generated by the underlying transport, and opaque.Addresses can be used as destination in the Send operation. |
| getLog | | abstract protected Log getLog()(Code) | | |
| getNumMessages | | public int getNumMessages()(Code) | | Returns the number of messages that are waiting. Those messages can be
removed by
Channel.receive(long) . Note that this number could change after
calling this method and before calling receive() (e.g. the latter
method might be called by a different thread).
The number of messages on the queue, or -1 if the queue/channelis closed/disconnected. |
| getOpt | | abstract public Object getOpt(int option)(Code) | | Gets an option. This method can be called on an unconnected channel. Calling this
method on a closed channel returns null.
Parameters:
option - The option to be returned. The object associated with an option. |
| getState | | abstract public boolean getState(Address target, long timeout) throws ChannelNotConnectedException, ChannelClosedException(Code) | | Retrieve the state of the group. Will usually contact the oldest group member to get
the state. When the method returns true, a SetStateEvent will have been
added to the channel's queue, causing receive() to return the state in one of
the next invocations. If false, no state will be retrieved by receive().
Parameters:
target - The address of the member from which the state is to be retrieved. If it isnull, the coordinator is contacted.
Parameters:
timeout - Milliseconds to wait for the response (0 = wait indefinitely). boolean True if the state was retrieved successfully, otherwise false.
exception:
ChannelNotConnectedException - The channel must be connected to receive messages.
exception:
ChannelClosedException - The channel is closed and therefore cannot be usedany longer. A new channel has to be created first. |
| getView | | abstract public View getView()(Code) | | Gets the current view. This does not retrieve a new view, use
receive() to do so. The view may only be available after a successful
connect(). The result of calling this method on an unconnected channel
is implementation defined (may return null). Calling it on a channel that is not
enabled to receive view events (via setOpt) returns
null. Calling this method on a closed channel returns a null view.
The current view. |
| isConnected | | abstract public boolean isConnected()(Code) | | Determines whether the channel is connected to a group. This implies it is open. If true is returned,
then the channel can be used to send and receive messages.
|
| isOpen | | abstract public boolean isOpen()(Code) | | Determines whether the channel is open;
i.e., the protocol stack has been created (may not be connected though).
|
| notifyChannelClosed | | protected void notifyChannelClosed(Channel c)(Code) | | |
| notifyChannelConnected | | protected void notifyChannelConnected(Channel c)(Code) | | |
| notifyChannelDisconnected | | protected void notifyChannelDisconnected(Channel c)(Code) | | |
| notifyChannelReconnected | | protected void notifyChannelReconnected(Address addr)(Code) | | |
| notifyChannelShunned | | protected void notifyChannelShunned()(Code) | | |
| open | | public void open() throws ChannelException(Code) | | Re-opens a closed channel. Throws an exception if the channel is already open. After this method
returns, connect() may be called to join a group. The address of this member will be different from
the previous incarnation.
|
| option2String | | public static String option2String(int option)(Code) | | |
| peek | | abstract public Object peek(long timeout) throws ChannelNotConnectedException, ChannelClosedException, TimeoutException(Code) | | Returns the next message, view, block, suspect or other event without removing
it from the queue.
Parameters:
timeout - Value in milliseconds. Value <= 0 means wait forever A Message, View, BlockEvent, SuspectEvent, GetStateEvent or SetStateEvent object,depending on what is on top of the internal queue.
exception:
ChannelNotConnectedException - The channel must be connected to receive messages.
exception:
ChannelClosedException - The channel is closed and therefore cannot be used any longer.A new channel has to be created first.
exception:
TimeoutException - Thrown when a timeout has occurred.
See Also: Channel.receive(long) |
| receive | | abstract public Object receive(long timeout) throws ChannelNotConnectedException, ChannelClosedException, TimeoutException(Code) | | Receives a message, a view change or a block event. By using setOpt, the
type of objects to be received can be determined (e.g., not views and blocks, just
messages).
The possible types returned can be:
Message. Normal message
Event. All other events (used by JChannel)
View. A view change.
BlockEvent. A block event indicating that a flush protocol has been started, and we should not
send any more messages. This event should be ack'ed by calling
org.jgroups.Channel.blockOk .
Any messages sent after blockOk() returns might get blocked until the flush protocol has completed.
UnblockEvent. An unblock event indicating that the flush protocol has completed and we can resume
sending messages
SuspectEvent. A notification of a suspected member.
GetStateEvent. The current state of the application should be
returned using ReturnState.
SetStateEvent. The state of a single/all members as requested previously
by having called Channel.getState(s).
ExitEvent. Signals that this member was forced to leave the group
(e.g., caused by the member being suspected.) The member can rejoin the group by calling
open(). If the AUTO_RECONNECT is set (see setOpt()), the reconnect will be done automatically.
The instanceof operator can be used to discriminate between different types
returned.
Parameters:
timeout - Value in milliseconds. Value <= 0 means wait forever A Message, View, BlockEvent, SuspectEvent, GetStateEvent, SetStateEvent orExitEvent, depending on what is on top of the internal queue.
exception:
ChannelNotConnectedException - The channel must be connected to receive messages.
exception:
ChannelClosedException - The channel is closed and therefore cannot be used any longer.A new channel has to be created first.
exception:
TimeoutException - Thrown when a timeout has occurred. |
| returnState | | abstract public void returnState(byte[] state)(Code) | | Called by the application is response to receiving a
getState() object when calling receive().
Parameters:
state - The state of the application as a byte buffer(to send over the network). |
| returnState | | abstract public void returnState(byte[] state, String state_id)(Code) | | Returns a given substate (state_id of null means return entire state)
|
| send | | abstract public void send(Message msg) throws ChannelNotConnectedException, ChannelClosedException(Code) | | Sends a message to a (unicast) destination. The message contains
- a destination address (Address). A
null address sends the message
to all group members.
- a source address. Can be left empty. Will be filled in by the protocol stack.
- a byte buffer. The message contents.
- several additional fields. They can be used by application programs (or patterns). E.g.
a message ID, a
oneway field which determines whether a response is
expected etc.
Parameters:
msg - The message to be sent. Destination and buffer should be set. A null destinationmeans to send to all group members.
exception:
ChannelNotConnectedException - The channel must be connected to send messages.
exception:
ChannelClosedException - The channel is closed and therefore cannot be used any longer.A new channel has to be created first. |
| send | | abstract public void send(Address dst, Address src, Serializable obj) throws ChannelNotConnectedException, ChannelClosedException(Code) | | Helper method. Will create a Message(dst, src, obj) and use send(Message).
Parameters:
dst - Destination address for message. If null, message will be sent to all current group members
Parameters:
src - Source (sender's) address. If null, it will be set by the protocol's transport layer beforebeing put on the wire. Can usually be set to null.
Parameters:
obj - Serializable object. Will be serialized into the byte buffer of the Message. If it is not serializable, the byte buffer will be null. |
| setChannelListener | | public void setChannelListener(ChannelListener channel_listener)(Code) | | Allows to be notified when a channel event such as connect, disconnect or close occurs.
E.g. a PullPushAdapter may choose to stop when the channel is closed, or to start when
it is opened.
|
| setOpt | | abstract public void setOpt(int option, Object value)(Code) | | Sets an option. The following options are currently recognized:
BLOCK. Turn the reception of BLOCK events on/off (value is Boolean).
Default is off
LOCAL. Receive its own broadcast messages to the group
(value is Boolean). Default is on.
AUTO_RECONNECT. Turn auto-reconnection on/off. If on, when a member if forced out
of a group (EXIT event), then we will reconnect.
AUTO_GETSTATE. Turn automatic fetching of state after an auto-reconnect on/off.
This also sets AUTO_RECONNECT to true (if not yet set).
This method can be called on an unconnected channel. Calling this method on a
closed channel has no effect.
|
| setReceiver | | public void setReceiver(Receiver r)(Code) | | Sets the receiver, which will handle all messages, view changes etc
|
| setUpHandler | | public void setUpHandler(UpHandler up_handler)(Code) | | When up_handler is set, all events will be passed to it directly. These will not be received
by the channel (except connect/disconnect, state retrieval and the like). This can be used by
building blocks on top of a channel; thus the channel is used as a pass-through medium, and
the building blocks take over some of the channel's tasks. However, tasks such as connection
management and state transfer is still handled by the channel.
|
| shutdown | | abstract protected void shutdown()(Code) | | Shuts down the channel without disconnecting if connected, stops all the threads
|
| startFlush | | abstract public boolean startFlush(long timeout, boolean automatic_resume)(Code) | | |
| stopFlush | | abstract public void stopFlush()(Code) | | |
|
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